. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. 124 INTESTINAL FLAGELLATES AND CILIATES cysted forms has very rarely been observed, and some writers have even gone so far as to say that it does not occur. It is well known that division into two individuals takes place after en- cystment, and Wenyon has recently expressed the opinion that if the division is completed before the cyst is expelled from the body of the host, the cyst may burst and liberate the two animals,. FiQ. 33. Giardia (or Lamblia) iniestinalis; A, side view (s. sucker-like depres- s
. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. 124 INTESTINAL FLAGELLATES AND CILIATES cysted forms has very rarely been observed, and some writers have even gone so far as to say that it does not occur. It is well known that division into two individuals takes place after en- cystment, and Wenyon has recently expressed the opinion that if the division is completed before the cyst is expelled from the body of the host, the cyst may burst and liberate the two animals,. FiQ. 33. Giardia (or Lamblia) iniestinalis; A, side view (s. sucker-like depres- sion); B, ventral view (par. b., parabasal bodies, n., nucleus); C, young cyst with four nuclei; D, mature cyst containing two parasites; E, end view of young cyst; F, parasite resting on epithelial cell. Figs. A-E, X 2000, after Wenyon; Fig. F, X 1000, after Grassi and SchewiakoS. the cysts thus serving as a means of multipHcation. Kofoid and Christiansen have recently succeeded in finding numerous individuals of an allied parasite of the mouse, Giardia muris, in process of division into two and also into four and eight indi- viduals, both in the free and in the encysted state. That a simi- lar process really occurs in the human parasite can hardly be doubted, both from its similarity to the mouse parasite and from the enormous numbers which may occur in an infected person at one time. The free active parasites become motionless and die soon after leaving the body of the host with the fseces, but encysted forms (Fig. 33C, D and E) may retain their vitaUty for a very long Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Chandler, Asa Crawford, 1891-. New York, J. Wiley
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